A/C randomly blows off pressure when Idling

Well, I'm expecting these are different A/C systems. So the fan clutch is old style belt driven mechanical. Not computer controlled, and high pressure specifications (not a colored switch) show it cuts off the compressor at 429PSI(I previously said 426 in error), and blow off is well over 500, as it hit 525PSI and had not yet blown off, before I shut it off. The thought of debris in the system is why I activated the compressor with the orifice tube out, high side open(low pressure switch jumped), and used my thumb to create pressure, then let it blow out freely. This was to make sure there was nothing backing up behind the Orifice tube causing this issue. Next, the pressure spike shows on the gauges, which are in the same aluminum assembly, so high and low are only separated by a single connection, which holds the orifice tube. No rubber lines in between, and if that were the cause, it would not show on the gauge.
The one time I was able to see it happen in the shop, it was freshly charged at idle, and the pressures began to climb. I watched it go to over 500psi, then heard (and felt) the fan begin to pull more air, and the pressures all dropped to normal.
Currently, with the new AC Delco high pressure transducer, it has cut the compressor instead of blowing off the pressure, but the last time was 2 days ago. Currently the system seems to be working normally most of the time, yet still occasionally has this failure. It seems to be an airflow issue. Like the fan clutch (which is new, attempting to fix this issue) just doesn't pull enough on occasion, but the truck itself never gets hot, and I can hear it kick in hard when the temp gets barely above the normal mark. This is just a drive you up the wall issue. But at least it's my truck instead of a customers. Lol. This has been going on quite awhile, but I previously didn't know the cause. Since it would only tell my on the MODIS scanner that under that PID that the a/c was "not granted" but did not tell me why. After it blew off the pressure, I finally saw what was happening, and have a better understanding of the system. But still have no answer as to why.

Orifice tube can cause high pressures. As it it the dividing point between high and low sides, and is actually what gives you a pressure difference. On an expansion block system, that is what does it.
If you have a plugged O-tube the pressure will definitely be high. But all the time. Not random.

WRENCHTECH Quote-"No it can't because with no refrigerant flow through it, the compressor has nothing to pump up pressure with and the result extremely low suction side pressure and stagnant head pressure. I live in south Florida and have specialized in AC repairs most of my career. "
https://www.freeasestudyguides.com/ac-clogged-orifice-tube.html
"A clogged orifice tube is typically caused by compressor failure. When this happens, little pieces of metal and aluminum shrapnel will be found in the tube's screen filter. If the filter’s filled with white or brownish debris, the desiccant bag in the accumulator has broken, sending desiccant throughout the system. This restriction will cause high high side system pressures. Restrictions result in frost forming around the restricted area."

or you might like this one better...https://www.fixmyoldride.com/orifice-tube-automotive-air-conditioning.html
"More specifically the low side will show below normal low pressure readings. An inexperienced mechanic just reading the low pressure side might think that the Freon level is low. However, when you have a high side gauge connected and the tube is blocked you'll see higher than normal high side pressure readings.

A low pressure reading below specification and high pressure readings above what’s expected is a sign that this orifice tube needs a visual inspection. This means the system must be recovered and the part physically removed."

I also have worked on these systems most of my life...the above quotes are from the web sites noted...you don't have to take my word for it...but the low side can go well below zero with a plugged system, and the high side be higher than normal at the same time. I am an ASE master technician, and have been for the last 27years...I'm not a rookie to this game.

As far as the condenser, the temperature readings were uniform across the surface. No hot or cold spots. I am not sure I am following what you are suggesting about the condenser. Are you talking internal or external blockage? Externally, it is pretty clean with no blockages, and internally should show with a heat gun. And it does not.
Was your suggestion that the condenser is designed the same as a radiator? Where it can flow freely wherever it wants? Essentially with tanks on each end? It does look similar to that, but both inlet and outlet are on the same end, so there must be divisions that are not visible. As shown in the image. There are baffles in the design This image shows 3 sections, but to say it could be 90% plugged and still have normal flow seems odd to me.

Roy, that is the issue.I can pretty much never get it to act up in the shop. When I did get it to do so, the one time I killed it before it blew off at about 525 psi, the other is when the fan started pulling more air, and the pressures dropped to normal.
So no, the condenser has not been replaced, but I did use a temp gun and confirmed it was pretty even across the whole surface. (But again, this is when it was acting normal.)
It seems it MUST be air flow. But it is not often enough to know when it is going act up.
As stated. At idle, after a short drive, cold or hot. Usually after sitting at a stop light for a few minutes. Currently it goes to what I refer to as "swamp cooler mode" AC gets humid, and warm, as the compressor cuts out. Until I start moving again. Then back on and normal cooling again.(Note-condenser and radiator have been blown out, but were just mildly dusty.)

Yes. Long thread, but I had previously noted that the fan clutch is brand new.
What it acts like is that, as the old school clutches did, it is freewheeling too much, after it has run a little bit. This will even happen right after startup. On occasion, I have started it up and driven out of my shop driveway(so about 100 or so yards) and stopped at the signal, where it blew off the pressure. Other times I have driven days without an issue, then it just does it. So while it is unpredictable as to when, the circumstances are always the same. Pulled up to an extended stop. Yes, it is new Freon, and the machine is pretty new.6 to 8 months old.
Now that it is back to occasionally cutting the compressor, it is not quite so annoying as losing Freon. But it still seems there must be an answer to this issue.

That may be a consideration, although it was replaced in order to see if that was it. And there was nothing wrong with the last one that I know of. Just throwing things at it to try to stop this issue. Same reason I replaced the accumulator, and orifice tube. Currently is has not cut out again for a couple days. It is an odd creature.I'll check back and keep you posted.